Why compare? Bitcoin is a unique asset. Gold, too. Why compare them to each other?
Because someone is arguing the scarcity of the Bitcoin is not on purpose and thus Bitcoin was never designed to replace fiat one day.
scarcity is not going to prevent bitcoin from being used by every human on earth as a currency because scarcity mainly means that bitcoin has a clear cap on its supply and a clear predefined supply production that is not going to change like the way fiat does on the whim of the government.
but at the same time i have never read anywhere that Satoshi claimed that bitcoin is to replace fiat though.